Abstract
In the robust image watermarking framework, watermarks are usually embedded in the direct current (DC) coefficients in discrete cosine transform (DCT) domain, since the DC coefficients have a larger perceptual capacity than any alternating current (AC) coefficients. However, DC coefficients are also excluded from watermark embedding with the consideration of avoiding block artifacts in watermarked images. Studies on human vision suggest that perceptual characteristics can achieve better image fidelity. With this perspective, we propose a novel spatial–perceptual embedding for a color image watermarking algorithm that includes the robust just-noticeable difference (JND) guidance. The logarithmic transform function is used for quantization embedding. Meanwhile, an adaptive quantization step is modeled by incorporating the partial AC coefficients. The novelty and effectiveness of the proposed framework are supported by JND perceptual guidance for spatial pixels. Experiments validate that the proposed watermarking algorithm produces a significantly better performance.
Highlights
Nowadays, with the rapid development of information technology, the storage, replication, and dissemination of digital multimedia have become easier
Das et al [11] proposed a method that uses the relationship between blocks to change the discrete cosine transform (DCT) coefficients to achieve the purpose of embedding watermark information, but the method needs to improve the performance of resisting noise attacks
One part of the watermark message m is embedded into the direct current (DC) coefficient by Equations (18)–(20); 8: Use the just-noticeable difference (JND) model to guide the amount of modification to each pixel in each image block by Equation (22); 9: Generate the modified block B∗ ; 10: end for 11: Generate the watermarked image Y by collecting all the modified blocks B∗ ; 12: Generate the watermarked color image by concatenating the modified Y with the Cb and Cr image channel and convert the color space from YCbCr to RGB by Equation (23); 13: return Watermarked image Iw ; 3.2
Summary
With the rapid development of information technology, the storage, replication, and dissemination of digital multimedia have become easier. The spatial domain watermarking achieves the purpose of embedding watermark information by directly modifying the image pixel values. Lin et al [16] embedded watermark information into a selected image block by varying the value of a low-frequency DCT coefficient; the method has good performance to resist the JPEG compression, the watermarked image’s visual quality has some distortion. In order to fix the problems discussed above, a robust DCT-domain JND model is presented and transformed to the spatial domain It can estimate the explicit JND threshold for the individual pixel. As the partial AC values are introduced to classify the block types and watermark embedding can alter the original image, the corresponding values in the proposed DCT-based JND profile would be set to zero, which can compensate for the robustness.
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